When you say passphrase, do you mean a password which you created? Or a randomized passphrase which was created for you? If the former, it could well be crackable. If the latter, there’s really not much hope at all.

The only way to recover a password, short of remembering it or finding a backup, would be to crack it. Unless you have some cracking knowledge, you’ll need to find a trusted person or service to attempt the crack for you. If you can remember anything about the password (you say it starts with a 6?) such as the length or any likely words, numbers or characters it contains, that could help a lot.